Sample Preparation Methods
Analysis are performed on pressed pellets for trace elements and fusion glass disks for major elements.
Pressed pellets are prepared using 40 mm aluminium cups filled with Boric acid crystals as binder. Finely powdered sample (-300 mesh) is sprinkled over boric acid and pressed in a 40 ton hydraulic press to produce a circular 40 mm disk. The pressed powder pellets allows trace element determinations, with limits of detection up to 1 ppm for selected elements. The elements determined presently in our lab are K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Rb, Sr, Y, Zr, Nb, Ba, Ce, Pb, Th. Light elements like Si, Al, Mg and Na are less precise by this method. All major and trace elements are determined on sample pellets for which fused glass disk can not be made (for e.g. river and marine sediments, soils etc.).
Fused glass Disk is prepared on a Claisse Fluxy instrument in the sample preparation lab of CESS. One gram of finely powdered sample is mixed with 5 gram of flux (LiT/LiM/LiBR 49.75/49.75/0.50, Pure) and fused in a platinum crucible. The fluxer is microprocessor controlled and uses LPG and in controlled manner raises the temperature up to 1000°C. It has built in programmes for different sample types. Rotating and stirring of crucible for uniform mixing and pouring the fused liquid on to a platinum mold to produce 30 mm glass disk is done automatically. It is also possible to create need based programmes with different gas flow, crucible tilt, mixing speed and length of each step
Fused disks are excellent for analysing major elements as it reduces matrix effects; eliminates particle size effects; and provides a homogeneous specimen. Samples which contain higher than normal concentrations of elements like lead, tin, arsenic and/or antimony (as they can seriously damage the platinum ware) and samples which contain organic matter are not suitable for this method of sample preparation. Elements determined by this method are Na, Mg, Al, Si, P, K, Ca, Ti, Mn, and Fe.